Influenza surveillance data from Africa to inform tailored vaccination programmes
Authors: Clement Meseko, Asabe Dzikwi-Emennaa
Journal: The Lancet Global Health (2023)

Sustained influenza surveillance and analysis of surveillance data are important steps in the characterisation of trends and patterns of seasonal influenza epidemics. The information generated can be used to inform rational regional and national vaccination policies. Influenza viruses—including subtypes influenza A/H1 and A/H3, and, to lesser extents, influenza B and C—cause yearly outbreaks in humans with varying degrees of morbidity and mortality in the temperate and tropical climes.1Kumar B Asha K Khanna M Ronsard L Meseko CA Sanicas M The emerging influenza virus threat: status and new prospects for its therapy and control.Arch Virol. 2018; 163: 831-844Crossref PubMed Scopus (52) Google Scholar Local climatic and ecological conditions contribute to the intensity and frequency of virus circulation and result in annual epidemics, often reported in temperate regions.2Tamerius JD Shaman J Alonso WJ et al.Environmental predictors of seasonal influenza epidemics across temperate and tropical climates.PLoS Pathog. 2013; 9e1003194Crossref PubMed Google Scholar This pattern of influenza transmission has been well studied in the temperate zones,3Azziz Baumgartner E Dao CN Nasreen S et al.Seasonality, timing, and climate drivers of influenza activity worldwide.J Infect Dis. 2012; 206: 838-846Crossref PubMed Scopus (189) Google Scholar, 4Young BE Chen M Influenza in temperate and tropical Asia: a review of epidemiology and vaccinology.Hum Vaccin Immunother. 2020; 16: 1659-1667Crossref PubMed Scopus (17) Google Scholar and there is a tendency to extrapolate such data for defining influenza activity in other regions. However, there are differences with respect to circulating strains, seasons, and patterns between and within continents, especially in tropical and subtropical Africa, as elaborated in a study by Ledor S Igboh and colleagues in The Lancet Global Health,5Igboh LS Roguski K Marcenac P et al.Timing of seasonal influenza epidemics for 25 countries in Africa during 2010–19: a retrospective analysis.Lancet Glob Health. 2023; 11: e729-e739Summary Full Text Full Text PDF Scopus (1) Google Scholar which succinctly describes epidemic periods that are peculiar to African countries. Igboh and colleagues' study is an incisive contribution to the literature and fills some of the knowledge gaps on influenza epidemic patterns in Africa. The epidemic data analysed also showed important diversity in the regions studied and highlight the non-homogeneous nature of influenza epidemics, which the authors categorise into five complex patterns based on northern to southern hemisphere epidemic trends. Africa is the second largest continent, sprawling across the equator between latitudes 37° north and 35° south. Countries at higher latitudes north of the equator show a northern hemisphere pattern and countries at higher latitudes south of the equator show a southern hemisphere pattern, but there are also microvariations in the pattern and that have been well described in this study. Notably, some countries showed a bimodal northern and southern hemisphere pattern, while some showed mixtures of patterns, with differences in epidemic thresholds even between countries. This report has been able to disaggregate the complexities and revealed influenza epidemic patterns for 25 countries in Africa. Previously, many tropical countries have used vaccines that seemed out of phase with their dominant influenza epidemic pattern. The key messages of this work are that influenza epidemics in Africa are heterogeneous and that even the northern versus southern hemisphere geographical paradigm for classification of predominance of influenza activity is imperfect. The different patterns of influenza epidemic should inform influenza control responses, and surveillance data, rather than geography, should guide timing of vaccination campaigns and vaccine formulation. Furthermore, the study emphasises the importance of strengthening year-round sentinel surveillance to generate evidence-based classifications of epidemic patterns. The study did not identify prevailing influenza genotypes and subtypes, and this was acknowledged as study limitation. Influenza viruses phenotypically exist in multiple subtypes. It is not enough to describe influenza virologically without defining whether it is influenza A, B, or C. Furthermore, influenza diversity extends to numerous possible combinations of H and N glycoproteins (subtypes), and circulation of genetically diverse influenza viruses can affect vaccine effectiveness.6Tenforde MW Kondor RJG Chung JR et al.Effect of antigenic drift on influenza vaccine effectiveness in the United States—2019–2020.Clin Infect Dis. 2021; 73: e4244-e4250Crossref PubMed Scopus (45) Google Scholar The success of preventive vaccination against influenza in humans is, therefore, predicated on the selection of fit for purpose vaccine candidates. The WHO Global Influenza Surveillance and Response network, from which most of the surveillance data in this analysis were obtained, provides information on circulating influenza strains. Given the constant evolution of influenza viruses, periodic review of surveillance data to update the viruses targeted by influenza vaccines is necessary for vaccine effectiveness;7Shao W Li X Goraya MU Wang S Chen JL Evolution of Influenza A Virus by Mutation and Re-Assortment.Int J Mol Sci. 2017; 181650Crossref Scopus (168) Google Scholar influenza data from any region will not be complete or optimal to inform vaccine composition if they are not specific about influenza subtypes (eg, H1N1 and H3N2 subtypes of influenza A). Disaggregation of influenza epidemic seasons and biological data from regions of the world including Africa can provide crucial information on circulating human and zoonotic influenza for vaccine formulation.8World Organisation for Animal HealthOFFLU collaboration in the WHO influenza vaccine virus selection process.https://bulletin.woah.org/?panorama=03-3-2020-2_offluDate accessed: March 5, 2023Google Scholar, 9WHORecommended composition of influenza virus vaccines for use in the 2023–2024 northern hemisphere influenza season.https://www.who.int/publications/m/item/recommended-composition-of-influenza-virus-vaccines-for-use-in-the-2023-2024-northern-hemisphere-influenza-seasonDate accessed: March 5, 2023Google Scholar Hospital data on circulating influenza viruses are important in the short-term selection of influenza vaccine candidates. Data obtained at the animal–human interface on emerging strains should also be integrated into evidence-based approaches to influenza control, including vaccine selection.10Meseko CA Heidari A Odaibo GN Olaleye DO Complete genome sequencing of H1N1pdm09 swine influenza isolates from Nigeria reveals likely reverse zoonotic transmission at the human-animal interface in intensive piggery.Infect Ecol Epidemiol. 2019; 91696632PubMed Google Scholar We declare no competing interests. Timing of seasonal influenza epidemics for 25 countries in Africa during 2010–19: a retrospective analysisMost countries had identifiable influenza epidemic periods that could be used to inform authorities of non-seasonal and seasonal influenza activity, guide vaccine timing, and promote timely interventions. Full-Text PDF Open Access